Discussion

HD is a hereditary neurodegenerative condition caused by a cytosine–adenine–guanine (CAG) repeat expansion in the HTT gene on the short arm of chromosome 4, with consequent production and accumulation of mutant huntingtin protein, which causes neuronal dysfunction and death.2 It is clinically characterised by a triad of motor dysfunction with involuntary movements and loss of voluntary control, cognitive deterioration and psychiatric problems.2

Seizures are common in juvenile-onset HD2 but are no more prevalent in adult-onset HD than in the general population. However, neuropsychiatric symptoms are common in early HD and can involve several different complaints,2 including dissociative phenomena.

In our experience, many patients experience functional neurological symptoms soon after manifesting a HD diagnosis—most likely because of increased disease-related anxiety and the inevitable severe stress that accompanies such a diagnosis. In the general population, psychogenic non-epileptic seizures and psychogenic movement disorders are among the most frequent psychologically-mediated syndromes seen by neurologists,3 and this is also our experience in the HD clinic. It is often difficult to distinguish between psychogenic movement disorders and psychogenic non-epileptic seizures, since both share causative factors and clinical features; some authors classify both conditions under the same spectrum.3 In this particular case, the altered higher mental function and the complexity of the movements made psychogenic non-epileptic seizures more likely.

Psychogenic non-epileptic seizures or dissociative seizures occur in 10–20% of people diagnosed with epilepsy.4 They can be clinically similar to any kind of epileptic seizure but are of psychological origin rather than being caused by hypersynchronous discharges in the brain. Attacks that resemble complex partial seizures are a relatively rare manifestation of psychogenic non-epileptic seizures but, in our experience, patients with HD can report any kind of epilepsy-like attack. It remains to be seen whether complex partial seizure-like attacks are more common in this population. Psychogenic non-epileptic seizures are considered to be an abnormal coping mechanism in the spectrum of dissociation. Indeed, patients with this condition have stronger connectivity between brain areas associated with emotion (insula), executive (inferior frontal gyrus and parietal cortex) and movement control (precentral sulcus),5 a pattern also observed in conversion disorders.

Although psychogenic non-epileptic seizures are most frequent in women in their 20s and 30s, they can occur in anyone.1 There is a previous history of psychological trauma or psychiatric co-morbidities in approximately 70% of patients.1 Up to half of patients have a precipitating life event.1 The semiology of psychogenic non-epileptic seizures can resemble most types of epileptic seizures but some aspects may increase the clinical suspicion: triggering by psychological stress, long duration, fluctuating course, asynchronous movements, pelvic thrusting, forced eye closure, ictal crying, memory recall and signs of emotional distress.1 ,6

The diagnostic gold standard is video EEG, with the absence of ictal electroencephalographic abnormalities before, during and after the attack.1 The use of this technique is obligatory to make a documented diagnosis based on the ILAE criteria.1 Nevertheless, it is possible to establish the diagnosis with a lower degree of certainty. A clinically established diagnosis should be made when a conventional ictal EEG detects no abnormalities and the semiology is compatible with psychogenic non-epileptic seizures; a normal interictal EEG and a clinically witnessed event or clinically reviewed video-recording of an event suffice to allow a probable diagnosis; and finally, at the lower end of diagnostic certainty, a possible diagnosis needs a normal interictal EEG and a witness or self-reported description of a compatible event.1

These non-epileptic attacks can have adverse quality-of-life consequences and a high rate of recurrence.7 Thankfully, early and accurate recognition of psychogenic non-epileptic seizures improves the prognosis.8 The treatment plan should encompass discussing and explaining the diagnosis to the patient and carers, withdrawal of antiepileptic drugs with special attention to discontinuation syndromes, and psychiatric and/or psychological interventions.6